Along with the advanced computerization and multimedia trends in the society and needs for high functions to information processors, high-speed devices including LSI (Large Scale Integrated Circuit) and memories whose operating frequency exceeds several GHz have been developed continuously. Further, electronic devices have become more compact, and these high-speed devices are packaged in electronic devices at high density. Along with the trends toward high-speed and downsizing, electric noise such as conduction and unnecessary electromagnetic radiation from electronic devices tend to become of high level and high bandwidth. These electric noises not merely cause malfunction in their own circuits, but also cause adverse effects to other electronic devices including misoperation and jamming in receiving broadcasting radio waves. Accordingly, it has been an important subject to develop products with few electric noises such as conduction or unnecessary electromagnetic radiation from devices.
Currently, with regard to the noise countermeasures of electronic devices, since it has been difficult to clarify the relation between circuit operations and noise occurrence, efforts have been made through stopgap-measure like countermeasures after completion of products with conspicuous noise problems, and product designs to take large margins to noises. However, along with the increased noise level in high-speed and high-density electronic devices, increased time and costs in noise countermeasures by the stopgap-measure like countermeasures after completion of products have come to unignorable. Further, by the product designs to take large margins to noises, it has become difficult to satisfy the requirements for compact product size and low costs. Under such circumstances, movements have become active regarding problems of the EMC (Electromagnetic Compatibility) and EMI (Electromagnetic Interference) as design problems, and starting the approach against them from the initial stage of product developments. This is to clarify the cause of noise occurrence in electronic devices and perform product designs at a more essential level in consideration of countermeasures against noises.
Meanwhile, the inventors of the present invention have searched prior art documents about the unnecessary electromagnetic radiation countermeasure technologies, on the basis of the result of the present invention. As a result, the following documents were extracted.
In Japanese Patent Application Laid-Open Publication No. H10-223997, a technology is disclosed where “in a printed-wiring substrate, to a power-supply pattern of an IC separated from a main power supply, a ground pattern is formed on a back surface of the substrate so as to oppose the power-supply pattern, so that electromagnetic wave radiation noises from the printed-wiring substrate are reduced.”
In Japanese Patent Application Laid-Open Publication No. 2003-297963, a technology is disclosed where “in a multilayer circuit substrate comprising: a layer to mount an IC; a layer including a power-supply pattern for an external power supply to which an external power supply is connected; and a layer including a power-supply wiring and a ground wiring to which both the terminals of a bypass capacitor to an IC power-supply terminal are connected on the surface opposite to the layer to mount an IC, wherein the power-supply pattern for IC power-supply terminal to which the IC power-supply terminal is connected in any layer is arranged so as to be spatially separate from the power-supply pattern for external power supply; the power-supply pattern for external power supply is connected to the power-supply wiring for the bypass capacitor; and the power-supply wiring for the bypass capacitor is connected to the power-supply pattern for the IC power-supply terminal so that unnecessary radiation noises that occurs due to high frequency current occurring at the IC power-supply terminal transmits from the power-supply pattern for external power supply to the entire substrate are reduced.”
In Japanese Patent Application Laid-Open Publication No. 2001-267702, a technology is disclosed where “in a printed-wiring substrate comprising a plurality of layers including: a layer including a mounting surface onto which semiconductor parts having a plurality of input power-supply terminals to input identical voltage are equipped; and a layer including a first power-supply area to which an external power supply is connected, wherein a second power-supply area whose outside dimension is smaller than the outside dimension of the semiconductor parts arranged independently from the first power-supply area and supplies electric power to the plurality of input power-supply terminals via a filter portion to reduce noises from the first power-supply area is arranged, thereby reducing noise components at the low frequency side supplied from the external, and also radiation noise itself at the high frequency side radiated from the second power-supply area itself can be suppressed to be small, and radiation noises can be reduced to be very small as a whole.”
Patent Document 1: Japanese Patent Application Laid-Open Publication No. H10-223997
Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2003-297963
Patent Document 3: Japanese Patent Application Laid-Open
Publication No. 2001-267702